Microphone device



0CL'31, 1944c E. w. ROGERS 2,361,656

MICROPHONE DEVICE Filed Feb. 9, 19- 12 4 Patented Oct. 31, 1944MICROPHONE DEVICE Ernest William Rogers, Hayes, England, assignor toRe'dlflusion Limited, London, England, a 4 company of Great BritainApplication February 9, 1942, Serial No. 430,127 In Great BritainFebruary 18, 1941 17 Claims.

This invention relates to microphone devices and has for its primaryobject to provide such devices and microphone systems whereby soundwaves emanating from positions which are angularly displaced in relationto the location of the microphone, selectively can be received, thuspermitting for example, substantially complete attenuation of sound'waves from one sound source whilst obtaining satisfactory reception ofsound waves from another but angularlydisplaced source.

Microphones according to the invention can be employed for a variety ofpurposes such, for instance, as a voice pick-up for film studio workwhen it is desired to eliminate pick-up of interfering sound waves fromcamera or other mechanism. The devices can also be used withconsiderable success for determining the direction of a sound source or,to be more precise, the direction of approach of sound waves, Withoutinterference from other sound waves approaching from an angularlydisplaced direction.

Many known forms of electro-acoustic means possess directionalproperties and those of the ribbon velocity type have quite pronounceddirectional characteristics. Even so, in general the response of suchdirectional microphones is too broad to obtain in practice a sharplydefined directional effect, except possibly in cases-mot oftenoccurringwhere the approaching sound wave has, at least in effect, theform of a narrow beam or emanates from a point source. Furthermore, thesensitivity of these known devices to extraneous noise remains undulyhigh so that in cases where sound waves of large amplitude are beingradiated from a close-by source, and even though such source may belocated in the direction favourable for minimum microphone response, thepick-up or such unwanted sound may seriously encroach upon or evendominate over the pick-up of the Wanted sound Waves, therebyjeapordising if not completely annihilating the directional propertiesof the device. An arrangement of two separate microphone devices forsound location purposes may, in certain circumstances, give reasonablygood sense of direction but the above mentioned disadvantages withrespect to extraneous noise still exist, and irrespective of theirelectrical interconnection, phasing troubles are introduced.

Now, a microphone device according to the broadest aspect of thisinvention comprises, in combination as a unitary structure, twoelectroacoustic means of the kind exhibiting a pronounced directionaleffect, said means being so relatively disposed that their respectivelines of maximum sensitivity are angularly separated.

In more elaborate embodiments of the invention more than twoelectro-acoustic means are grouped to form a microphone device and insuch cases some of the said means may be so disposed that theirrespective lines of maximum sensitivity are substantially parallel. Thusfor example,

four electro-acoustic means can be assembled to P each group of suchmeans having relatively parallel lines of maximum sensitivity, can beob-' tained separately, thus enabling a variety of phase and/oramplitude modified combinations readily to be made through theintermediary of suitable equipment which may include space dischargevalve amplifying means.

One particular practical embodiment comprises four electro-acousticmeans of the ribbon type arranged to form a single and compactmicrophone device possessing variable directional properties of a veryhigh order of efficiency. In order that the invention more readily maybe understood this particular embodiment will now be described, by wayof example, with reference to the accompanying drawing, wherein- Fig. 1shows a side elevation of the microphone device.

Fig. 2 is a plan view of Fig. 1.

Fig. 3 is a sectional plan taken on the line 3-3 of Fig. 1.

Fig. 4 shows diagrammatically one embodiment of a mixing and amplifyingcircuit for the signals obtained from such a microphone device.

Referring to Figs. l-3 it will be seen that the magnetic system of thisdevice comprises a central common pole member 5 of cruciform section andfour pole-pieces 6-9 symmetrically arranged therearound, one pole piecebeing disposed op posite each arm of the cruciform section but spacedtherefrom to provide a magnetic gap. In each of these four magnetic gapsthere is mounted a vibratory element consisting of a corrugated ribbon|D-I3 respectively of aluminium or other light weight conductor, theseveral ribbons extending along the common pole member 5 in radialplanes through the axis of the common pole member. The poles areapertured at f 4 to provide a direct air path, between the oppositesides of each sound wave responsive ribbon, of

whilst the two planes containing the respective pairs of ribbons are atright angles. Thus two pairs of ribbon microphone means are provided andtheir relative arrangement'is such that the respective lines of maximumsensitivity for one diametrically opposed pair are normal to thecorresponding lines of the other diametrically opposed pair.

cated at the centre of the assembly and that cooperatively the two pairsresemble, in action, two single ribbons so centrally disposed butcontained in relatively normal planes. It appears that this theory holdsgood for the high audio frequencies so long as the ribbons are closelyspaced and in this respect it should be noted that the constructionalarrangement described is conducive to close spacing of the ribbons. Itshould also be noted that the multiplicityof symmetrically arranged polepieces results in a highly efficient magnet system.

One manner of utilising such a microphone device consists in feeding thetwo separate outputs to a mixing circuit. An example of such amicrophone system is shown in Fig. 4 and comprises a thermionic valveamplifier having two valves VI and V2 provided with a common anode loadimpedance RI and separate coupling means heposition for minimumsensitivity to the said wave and very little pick-up, if any, willresult, except if the sound wave approaches as a fairly broad beam, inwhich case the small amount of pick-up will be equal for each pair ofribbons. However such pick-up can be rendered completely ineffective bycancelling out the response of one pair tween the respective controlgrids and the microphone device M. Such coupling is made by audiotransformers Tl, T2 across the secondary winding of each of which thereis connected a potentiometer R2, R3 respectively. The valves VI and V2are suitably biased by providing a cathode resistor R4 across which isconnected a condenser CI. The output from this mixing circuit isobtained by way of a condenser C2. Thus, separately variable attenuationof the output from each pair of ribbons can be efiected by means of thepotentiometers, whilst, by providing a centre tapping on the secondarywinding of each transformer, as shown, and connecting this tapping pointto the valve cathodes or earth, operation of either of thepotentiometers will bring about a modification of the phase relationshipof the signals applied to the input grids.

The microphone device in combination with this or an equivalent mixingsystem can be made to behave in various'ways. Thus each coupled pair ofribbons can be employed separately. Alternatively, both pairs of ribbonscan be employed with their outputs in phase or 180 out of phase and withthe same degree of attenuation or different degrees of attenuation.Furthermore, the

output of one coupled pair of ribbons can be employed to cancel theoutput of the other coupled pair of ribbons.

If the device is so positioned that all four ribbons are in alignmentwith the direction of approach'of a sound wave (that is to say the soundwaves travel along the length of the ribbon) and ignoring reflections orother disturbances from nearbybodies, each pair of ribbons will be in aof ribbons by the response of the other pair thus leaving each pair ofribbons free to receive sound waves coming from other angularly disposeddirections.

The microphone device can also be so positioned for use that one pair ofribbons is located for minimum sensitivity with respect to an unwantedsound wave whilst the other ribbons will be more sensitive to such soundwave and a small fraction of their output can be employed to cancel outthe pick-up from the other pair. With such an arrangement sound wavescoming from a direction other than that of the unwanted sound waves willnot be subjected to cancellation and consequently can be received freeof interference from the unwanted sound waves.

According to a modified embodiment, means are provided whereby theoutput of each or more of four ribbons can be obtained separately and ifdesired such separate outputs can be passed to separate input channelsof a mixing circuit.

In another arrangement, the outputs from the separate electro-acousticmeans are paralleled and applied to a common input circuit of a valveamplifying equipment.

What I claim and desire to secure by Letters Patent is:

1. A microphone device comprising a central pole means, a plurality ofouter pole means arranged about said central pole means to form aplurality of angularly separated and elongated magnetic gaps allextending substantially parallel to the axis of said central pole, and asound wave responsive ribbon element in each of said gaps to formelectro-acoustic means, said ribbon elements being located in angularlyspaced planes, whereby the respective lines of maximum sensitivity ofthe plurality of electro-acoustic means are separated angularly.

2. A microphone device comprising a central pole means, a plurality ofouter pole means arranged about said central pole means to form aplurality of magnetic gaps, and a sound wave responsive ribbon elementin each of said gaps to form electro-acoustic means, said ribbonelements being located in planes at right angles to each other, wherebythe respective lines of maximum sensitivity of the plurality ofelectroacoustic means extend at right angles to one another.

3. A microphone device comprising a center pole member of cruciformcross section, four outer pole members cooperating with said center polemember to form four symmetrically disposed magnetic gaps, and a soundWave responsive ribbon element in each of said magnetic gaps to formelectro-acoustic means, said ribbon elements being arranged along thecentral pole member in angularly spaced planes, whereby the respectivelines of maximum sensitivity of at least two of the plurality ofelectro-acoustic means thus provided are separated angularly.

4. A microphone device comprising a central pole means, a plurality ofouter pole means arranged about said central pole means to form aplurality of magnetic gaps, a sound wave responsive ribbon element ineach of two of said gaps to form a pair of electro-acoustic means, saidribbon elements being so disposed that their respective lines of maximumsensitivity are substantially parallel, and a sound wave responsive"tionship with the said parallel lines of maximum sensitivity.

5. A microphone device comprising a central pole means, a plurality ofouter pole means arranged about said central pole means to form aplurality of magnetic gaps, a sound wave respon-' sive ribbon element ineach of two of said gaps to form a pair of electro-acoustic means, saidribbon elements being so disposed that their respective lines of maximumsensitivity are substantially parallel, and a sound wave responsiveribbon element in each of two other of said gaps to form two furtherelectro-acoustic means, the said latter two ribbon elements being sorelatively arranged that their respective lines of maximum sensitivityare substantially parallel but at right angles with respect to thecorresponding lines of the first mentioned two ribbon elements.

6. A microphone device comprising a central pole means, a plurality ofouter pole means arranged about said central pole means to form aplurality of magnetic gaps, and a sound wave responsive ribbon elementin each of said gaps to form electro-acoustic means, said ribbonelements each extending parallel to a common line and being sorelatively arranged that the respective lines of maximum sensitivity of"the plurality of electro-acoustic means thus provided are separatedangularly.

7. A microphone device comprising a common magnetic pole member, aplurality of pole members arranged about said common pole member to forma plurality of magnetic gaps, and a sound wave responsive ribbon elementin each of said gaps to form electro-acoustic means, said ribbonelements being so relatively arranged that the respective lines ofmaximum sensitivity of the plurality of electro-acoustic means thusprovided are separated angularly.

8. A microphone device comprising a common magnetic pole member, aplurality of pole members arranged about said common pole member to forma plurality of magnetic gaps, and a sound wave responsive ribbon elementin each of said gaps to form electro-acoustic means, said ribbonelements being so relatively arranged that the respective lines ofmaximum sensitivity of the plurality of electro-acoustic means thusprovided extend at right angles to one another.

9. A microphone device comprising a common magnetic pole member, aplurality of magnetic gaps arranged about said common pole member, and asound wave responsive ribbon element in each of said gaps to formelectro-acoustic means, said ribbon elements each extending parallel toa common axis and being so relatively arranged that the respective linesof maximum sensitivity of the plurality of electro-acoustic means areseparated angularly.

10. A microphone device comprising a magnetic structure having at leasttwo magnetic gaps,

and a sound wave responsive ribbon element in each of said gaps to formelectro-acoustic means,

and angularly displaced, whereby the respective lines of maximumsensitivity of the plurality of electro-acoustic means are separatedangularly.

11. A microphone device comprising a magnetic structure having at leasttwo magnetic gaps, and a sound wave responsive ribbon element in each ofsaid gaps to form electro-acoustic means, said ribbon elements beingarranged side by side and at right angles to each other, whereby therespective lines of maximum sensitivity of the plurality ofelectro-acoustic means extend at right angles to one another. a

12. A microphone device comprising a magnetic structure having at leasttwo laterally alined magnetic gaps, and a sound wave responsive ribbonelement in each of said gaps to form electro-acoustic means, said ribbonelements being laterally alined and angularly displaced, whereby therespective lines of maximum sensitivity of the plurality ofelectro-acoustic means are separated angularly.

13. A microphone device comprising a magnetic system having a centerpole member. a plurality of symmetrically disposed radially extendmgpole members each of which is spaced from said center pole member toprovide a magnetic gap, and a sound wave responsive ribbon element soarranged in each of said gaps that the respective lines of maximumsensitivity of the plurality of electro-acoustic means thus provided areseparated angularly. I

14. A microphone device comprising a magnetic system having a centerpole member, a plurality of symmetrically disposed radially extendingpole members each of which is spaced from said center pole member toprovide a magnetic gap, and a sound wave responsive ribbon element soarranged in each of said gaps that the respective lines of maximumsensitivity of the plurality of electro-acoustic means thus providedextend at right angles to one another.

15. A microphone device comprising-a common magnetic pole member, fourpole members symmetrically arranged about said common pole least twomagnetic gaps, a sound wave responsive ribbon element in each of saidgaps, said ribbon elements being arranged side by side in a mannersuchthat the respective lines of maximum sensitivity of the plurality of'electro-acoustic means thus provided are separated angularly, a

said ribbon elements being arranged side by side separate valveamplifying device for each of said electro-acoustic means, and a commonload impedan'ce provided for said valve devices.

17. A microphone system as recited in claim 16, in combination withmeans for adjusting the phase and amplitude of the voltage impressedupon one valve amplifier device independently of upon another valveamplifying device.

ERNEST WILLIAM ROGERS.

